1. Field of the Invention
The invention relates to a solenoid arrangement. The invention also relates to a valve arrangement.
2 Description of the Prior Art
The solenoid arrangement of this generic type is often used in fluidics as a drive for actuating hydraulic or pneumatic valves.
Actuation magnets in fluidics are usually of modular construction and have a pole tube which is fluid-tight except for a through opening for the tappet and in which the armature is movable. A coil body is slipped over the pole tube. The coil body is secured with a nut. A separating ring of nonmagnetic material is typically welded in place between a pole core segment and a tube segment of the pole tube. As a result, the magnetic field lines in the pole tube pass from the pole core segment to the armature. Only in that way can a working air gap filled with field lines develop.
Precisely with switching valves, solenoids of the simplest possible construction are employed. For example, German Patent Application 10 2008 030 748 of the present Applicant describes a pole tube which, in order to generate the requisite discontinuity between the pole core and the tube segment, has a reduced material thickness in the vicinity of the transition segment. In that case, a secondary magnetic flux through the transition segment is tolerated for the sake of simpler production of the pole tube. These pole tubes are also called thin—turned pole tubes, since the reducing in the material thickness is typically done by turning on a lathe. However—in comparison to the usable magnetic flux sent through the working air gap—that requires a considerable secondary flux. If a thin-turned pole tube is used instead of a conventional pole tube, the presumptive force loss for a solenoid is about 10%, on the condition that the coil capacity is identical. Moreover, solenoids with thin-turned pole tubes often have a force-stroke characteristic curve that is very unfavorable for the valve actuation, as the characteristic curve 42 for a conventional solenoid in FIG. 3 shows. The actuation force rises significantly just before the armature makes contact with the pole core. A fluidic valve, however, requires a sufficient actuation force over a greater stroke range.